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L2 Neural Circuits > Auditory System > Flashcards

Auditory System Flashcards

1
Q

What is sensing sound important for? (5)

A
  • Communication
  • Triggers emotion
  • Recognising what things are by their sound
  • 3D view of the world
  • Survival, escaping danger
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2
Q

What are the units of frequency?

A

Hertz (Hz)

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3
Q

What are the units of loudness (intensity)?

A

Decibels (dB)

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4
Q

What are the 3 sections of the ear?

A
  • Outer ear
  • Middle ear
  • Inner ear
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5
Q

How does sound travel across the middle ear?

A

Via the ossicles

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6
Q

What are the 3 chambers of the cochlea?

A
  • Scala vestibuli
  • Scala media
  • Scala tympani
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7
Q

What is the organ of Corti?

A

The sensory organ of the cochlea containing the hair cells

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8
Q

What is the innervation of the organ of Corti?

A

Auditory nerve fibres

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9
Q

Where is the organ of Corti located?

A

Sits on the basilar membrane inside the scala media

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10
Q

What are the features of the organ of Corti? (3)

A
  • Contains 3 rows of outer hair cells and 1 row of inner hair cells
  • Sits on the basilar membrane
  • Tectorial membrane sits over the top of the hair cells
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11
Q

What is the arrangement of the 3 chambers in the cochlear spiral?

A
  • Scala media in the middle
  • Scala vestibuli above
  • Scala tympani below
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12
Q

What is the composition of perilymph? (4)

A
  • Normal extracellular solution
  • Low K+
  • High Na+
  • Normal Ca2+
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13
Q

Which chambers of the cochlea contain perilymph?

A
  • Scala vestibuli
  • Scala tympani
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14
Q

What is the composition of endolymph? (3)

A
  • High K+
  • Low Ca2+
  • Low Na+
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15
Q

Which chambers of the cochlea contain endolymph?

A

Only the scala media

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16
Q

How is the high K+ content of the endolymph generated?

A

Cells in the stria vascularis actively pump K+ into the scala media

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17
Q

What is the endocochlear potential?

A

Positive potential of +80mV in the scala media compared to the other chambers

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18
Q

What is the resting membrane potential of the hair cells in the organ of Corti?

A

-60mV

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19
Q

What are the 2 types of hair cells?

A

Outer and inner hair cells

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20
Q

Why is the cochlea arranged in a spiral structure?

A
  • To extend the frequency range of hearing as much as possible
  • Fits more hair cells within the small space
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21
Q

What is the tonotopic organisation of the cochlea? (2)

A
  • Cells at the base respond to high frequency sounds, cells at the apex respond to low frequency sounds
  • This map is preserved throughout the auditory pathway into the brain
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22
Q

How is sound frequency encoded? (3)

A
  • Place-Frequency code
  • The brain interprets the frequency of a sound by the position of the hair cells that are activated
  • Frequency isn’t encoded in the firing pattern of the nerves as it is represented by location
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23
Q

What determines the cochlear tonotopicity?

A

The basilar membrane travelling wave which goes from base to apex

24
Q

What is the Characteristic Frequency (CF) location?

A

The location where the same sound frequency causes maximal movement of the basilar membrane

25
Q

Which part of the basilar membrane is maximally displaced by low frequency sound?

A

Apex

26
Q

Which part of the basilar membrane is maximally displaced by high frequency sound?

A

Base

27
Q

Which part of the basilar membrane is narrow and stiff?

A

Base

28
Q

Which part of the basilar membrane is wide and floppy?

A

Apex

29
Q

What determines the CF location of a sound?

A

Width and stiffness of the basilar membrane

30
Q

Why do high frequency sounds have a CF location at the base of the basilar membrane?

A

Short wavelength and low energy so don’t travel very far

31
Q

Why do low frequency sounds have a CF location at the apex of the basilar membrane?

A

Long wavelength and high energy so travel further

32
Q

What is the function of the inner hair cells? (2)

A
  • They are the primary sensory receptors of the auditory system
  • They encode all auditory information and pass it on to the nerve fibres
33
Q

What are the features of inner hair cells? (3)

A
  • Hair bundle of stereocilia on the apical surface
  • The shorter stereocilia have MET channels at their tips
  • MET channels on shorter stereocilia are connected to the taller ones by tip links which pull the channels open
34
Q

What are MET channels?

A

Mechanoelectrical Transducer Channels

35
Q

What ion channels do inner hair cells express? (2)

A
  • Voltage gated Ca2+ channels to trigger neurotransmitter release
  • Voltage gated K+ channels for repolarisation
36
Q

Why are inner hair cells connected to many afferent nerve fibres?

A

They are the main sensory receptors of the auditory system

37
Q

What happens in the inner hair cells at rest (no sound)? (4)

A
  • Slight tension on the tip links which opens some MET channels resulting in a resting current (ITRest)
  • K+ enters the cell from the endolymph down a large electrical gradient
  • K+ leaves the cell via K+ channels down a large concentration gradient into the surrounding perilymph
  • Some Ca2+ and therefore neurotransmitter is released, causing some resting activity in the afferent fibres (spontaneous rate)
38
Q

What kind of gradient allows K+ to enter the inner hair cells from the endolymph? (2)

A
  • Electrical gradient (endolymph is +80mV, hair cell resting potential is -60mV)
  • Endolymph and intracellular K+ is similar so not much of a concentration gradient
39
Q

What is the spontaneous rate?

A

The firing of the afferent nerve fibres in the absence of any sound stimulus

40
Q

What happens in the inner hair cells during excitatory stimulation? (5)

A
  • Shorter stereocilia are pulled towards the taller ones which pulls the tip links and opens the MET channels
  • Large MET current depolarises the hair cell
  • Ca2+ channels open and neurotransmitter is released
  • Increases the firing activity of the afferent nerve fibres above the resting level
  • Voltage gated K+ channels open and K+ exits down a concentration gradient into the surrounding perilymph causing repolarisation
41
Q

What happens in the inner hair cells during inhibitory stimulation? (5)

A
  • Taller stereocilia are pushed towards the shorter ones which reduces tension in the tip links and closes the MET channels
  • The cell hyperpolarises below its resting level
  • Little to no Ca2+ and neurotransmitter release
  • Firing of the afferent nerve fibres drops below the spontaneous rate
  • K+ channels remain open for longer to repolarise the cell
42
Q

What happens to an inner hair cell during a sustained sound? (3)

A
  • Hair bundle is moved back and forth
  • Creates a cycle of depolarisation and hyperpolarisation which matches the sound frequency
  • Generates pulses of neurotransmitter release and afferent activity
43
Q

What is the advantage of using K+ to both depolarise and repolarise the cell?

A

Rapid and energy efficient (no active transport needed to maintain gradients)

44
Q

What kind of gradient allows K+ to leave the inner hair cells into the perilymph?

A

Chemical gradient (high intracellular K+ and low K+ in the perilymph)

45
Q

What happens if the barrier between the endolymph and perilymph breaks down?

A

Causes deafness

46
Q

What is the function of outer hair cells?

A

Cochlear amplification

47
Q

What makes the outer hair cells electromotile?

A

They shorten and lengthen in response to sound

48
Q

Why do outer hair cells not have many afferent nerve fibres? (2)

A
  • They don’t have a main sensory role
  • Most of their innervation is from inhibitory efferent fibres from the brain
49
Q

What are the features of outer hair cells? (2)

A
  • V shaped hair bundle on the apical surface
  • Stereocilia work in the same way as the inner hair cells
50
Q

What ion channels are expressed by outer hair cells?

A

Mainly voltage gated K+ channels

51
Q

What molecule present in the cell membrane of outer hair cells allows them to change length?

A

Prestin

52
Q

What is the resting potential of outer hair cells?

A

-40mV

53
Q

What happens to outer hair cells during excitatory stimulation? (3)

A
  • Hair bundle is deflected towards the taller stereocilia
  • Cell depolarises
  • Shortens in length
54
Q

What happens to outer hair cells during inhbitory stimulation? (3)

A
  • Hair bundle is deflected towards the shorter stereocilia
  • Cell hyperpolarises below the resting potential
  • Gets longer
55
Q

How do the outer hair cells amplify sound? (2)

A
  • They act as positive feedback in the cochlea by increasing the movement of the basilar membrane over a narrow CF region
  • This increases the stimulation of the inner hair cells and increases their sensitivity
56
Q

What happens if you lose your outer hair cells?

A

Severe hearing loss but not deafness because you still have the inner hair cells and the basic tuning of the basilar membrane

L2 Neural Circuits (13 decks)

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